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<h2><a name="SECTION0019120000000000000000">
17.1.2 Popen Objects</a>
</h2>

<p>
Instances of the <tt class="class">Popen</tt> class have the following methods:

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3631' xml:id='l2h-3631' class="method">poll</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Check if child process has terminated.  Returns returncode
attribute.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3632' xml:id='l2h-3632' class="method">wait</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Wait for child process to terminate.  Returns returncode attribute.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3633' xml:id='l2h-3633' class="method">communicate</tt></b>(</nobr></td>
  <td><var>input=None</var>)</td></tr></table></dt>
<dd>
Interact with process: Send data to stdin.  Read data from stdout and
stderr, until end-of-file is reached.  Wait for process to terminate.
The optional <var>input</var> argument should be a string to be sent to the
child process, or <code>None</code>, if no data should be sent to the child.

<p>
communicate() returns a tuple (stdout, stderr).

<p>
<span class="note"><b class="label">Note:</b>
The data read is buffered in memory, so do not use this method
if the data size is large or unlimited.</span>
</dl>

<p>
The following attributes are also available:

<p>
<dl><dt><b><tt id='l2h-3634' xml:id='l2h-3634' class="member">stdin</tt></b></dt>
<dd>
If the <var>stdin</var> argument is <code>PIPE</code>, this attribute is a file
object that provides input to the child process.  Otherwise, it is
<code>None</code>.
</dl>

<p>
<dl><dt><b><tt id='l2h-3635' xml:id='l2h-3635' class="member">stdout</tt></b></dt>
<dd>
If the <var>stdout</var> argument is <code>PIPE</code>, this attribute is a file
object that provides output from the child process.  Otherwise, it is
<code>None</code>.
</dl>

<p>
<dl><dt><b><tt id='l2h-3636' xml:id='l2h-3636' class="member">stderr</tt></b></dt>
<dd>
If the <var>stderr</var> argument is <code>PIPE</code>, this attribute is file
object that provides error output from the child process.  Otherwise,
it is <code>None</code>.
</dl>

<p>
<dl><dt><b><tt id='l2h-3637' xml:id='l2h-3637' class="member">pid</tt></b></dt>
<dd>
The process ID of the child process.
</dl>

<p>
<dl><dt><b><tt id='l2h-3638' xml:id='l2h-3638' class="member">returncode</tt></b></dt>
<dd>
The child return code.  A <code>None</code> value indicates that the process
hasn't terminated yet.  A negative value -N indicates that the child
was terminated by signal N (<span class="Unix">Unix</span> only).
</dl>

<p>

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